1. Field of the Invention
The present invention generally relates to a transmission system for a land vehicle. More particularly, the present invention relates to a locking differential control system that either varies engine output or controls actuation of the locking mechanism based in part upon engine speed.
2. Description of the Related Art
As is well known, a differential gear used on land vehicles divides power provided to it between two axles, which usually power two individual wheels. Under normal driving conditions, it is desirable to divide the input power nonuniformly such that the outside wheel (i.e., the wheel to the outside of the turn) can rotate faster than the inside wheel. The differential accomplishes this by apportioning the input power unequally between the wheels, as needed.
However, when increased traction is desired, some differential gears are constructed with a mechanism that locks-out the differential function. In other words, the two axles will be connected to ensure that both wheels receive the same power. Such an arrangement is helpful when it is necessary to travel over ice, mud, rocks and other low-traction environments. It is helpful in these environments because it is not desirable that one wheel spins more freely than another, particularly when this spinning means that all of the power is going to the spinning wheel.
Engagement of the differential lock can be difficult at higher speeds and can be undesirable at even higher speeds. For instance, as the vehicle speed increases, it often takes longer for the differential to achieve a locked-up state. This lengthy process of locking eventually can shorten the life of the differential locking components. In addition, when operating at higher speeds, the benefits of the locked-differential are decreased and the handling of the vehicle can be adversely affected. Moreover, operation at higher speeds in a locked state can further reduce the life of the differential and its locking components.
Accordingly, an arrangement is desired in which the timing of differential lock-up can be controlled. In addition, an arrangement that can limit the speeds at which the differential can be locked-up is desired.
One aspect of the present invention involves a method of controlling operation of a locking differential. The method comprises detecting a vehicle speed and, regardless of operator demand for an actuation of the locking differential, inhibiting the actuation of the locking differential unless the detected vehicle speed is below a predetermined vehicle speed that allows locking of the locking differential.
Another aspect of the present invention involves a method of controlling a locking mechanism of a differential in an all terrain vehicle. The method comprises detecting a vehicle speed, comparing the detected speed to a high-speed threshold and a low-speed threshold, and inhibiting actuation of the locking mechanism if the detected speed exceeds the high-speed threshold.
An additional aspect of the present invention involves a method of controlling a locking mechanism of a differential in a land vehicle. The method comprises detecting an operational mode of a drive train of the vehicle, allowing actuation of the locking mechanism at any speed if the operational mode is one of a two-wheel drive mode or a four wheel drive with locked differential mode, and limiting actuation if the operational mode is a four wheel drive with unlocked differential mode, wherein limiting actuation comprises detecting an operational speed of the vehicle, comparing the operational speed with a first threshold and a second threshold and inhibiting operation of an actuator of the locking mechanism if the detected speed exceeds the second threshold speed, which second threshold speed is higher than a vehicle speed that allows locking of the locking mechanism.
Yet another aspect of the present invention involves a method of controlling a vehicle comprising a locking differential. The locking differential comprises an actuator and a locking mechanism with the actuator being adapted to move the locking mechanism into a locked state. The method comprises detecting a state of the locking differential, detecting the speed of the vehicle and automatically limiting an operating speed of the vehicle to a speed below a preset low-speed threshold if the detected state is not the locked state and the detected speed is below the low-speed threshold.
A further aspect of the present invention involves a method of controlling a vehicle comprising a locking differential. The method comprises detecting a vehicle speed, comparing the detected vehicle speed to a first threshold and a second threshold, the first threshold being lower than the second threshold. The method further comprises detecting when locking the locking differential is demanded and inhibiting operation of the locking differential or allowing normal operation of an engine or both if the detected vehicle speed is greater than the second threshold, adjusting operation of the engine to maintain a speed of the vehicle below the first threshold or allowing operation of the locking differential if the detected vehicle speed is less than or equal to the first threshold, and maintaining a previous operational state of the locking differential or maintaining a previous operational state of the engine if the detected vehicle speed is between the first threshold and the second threshold.